Bronopol

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption

Remarks:

adsorption

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study conducted in accordance with GLP.

Qualifier:

according to guideline

Guideline:

other: EPA Pesticide assessment Guideline 163-1

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Analytical monitoring:

yes

Details on matrix:

SOILS
- The following soils were used in the study:
(1) Sand (Colorado, USA) supplied by Compliance Services International, Tacoma, WA, USA and received by IRI on 17 December 1990
(2) Loamy sand (Georgia, USA) supplied by Landis International Inc., Valdosta, GA, USA and received by IRI on 5 February 1991
(3) Loam (Scotland, UK) supplied by the Scottish Agricultural College, Auchincruive, Scotland and received by IRI on 31 January 1991
(4) Clay loam (Scotland, UK) supplied by the Scottish Agricultural College and received by IRI on 31 January 1991

SOIL PREPARATION
On arrival at IRI, soils (a) and (b) were sieved through a 2 mm stainless steel mesh and samples despatched to the Scottish Agricultural College for measurement of pH, organic matter content, particle size distribution and cation exchange capacity. Soils (c) and (d) were similarly sieved and characterised by the Scottish Agricultural College prior to arrival at IRI.

PROPERTIES
- pH: sand: 8.2
loamy sand: 4.7
loam: 7.0
clay loam: 5.9
- Organic matter (%): sand: 0.10
loamy sand: 2.60
loam: 1.97
clay loam: 5.20
- % sand: sand: 96.8
loamy sand: 86.3
loam: 45.6
clay loam: 38.9
- % silt: sand: 1.4
loamy sand: 3.6
loam: 29.5
clay loam: 28.8
- % clay: sand: 1.8
loamy sand: 10.1
loam: 24.8
clay loam: 32.2

Key result

Type:

Koc

Value:

136.06

Remarks on result:

other: geo mean for adsorption in all four soil types

Type:

Koc

Value:

> 388.3 - < 1 416

Remarks on result:

other: Soil 1: sand

Type:

Koc

Value:

> 46.74 - < 61.97

Remarks on result:

other: Soil 2: loamy sand

Type:

Koc

Value:

> 170.5 - < 306

Remarks on result:

other: Soil 3: loam

Type:

Koc

Value:

> 36.82 - < 41.31

Remarks on result:

other: Soil 4: clay loam

Recovery of test material:

Total recoveries of radioactivity from solution and soil were 91.71 - 97.11 % (mean values) for the sand, loamy sand and clay loam soils (excluding the sand at the lowest concentration which gave a lower recovery of 88.77 %). Lower mean total recoveries (78.46 - 88.26 %) were obtained for the loam soil.

Transformation products:

yes

No.:

#1

No.:

#2

Details on results (Batch equilibrium method):

- The test material was instable under test conditions and the observed degradation was extensive and varied in the presence of the 4 soil types.
- Lower adsorption of radioactivity was observed in the clay loam, the soil with the highest organic clay content, and therefore, the greatest potential adsorptive capacity. This might be explained by the presence, in the more alkaline loam soil, of the relative non-polar products (A, B) which
might be potentially more adsorptive than the relative polar conversion product (C) formed in the more acidic clay loam soil.

Description of key information

Adsorption to solid soil phase is not expected. 

Additional information

Adsorption of ¹⁴C-Bronopol onto and desorption from four different soil types was investigated (Jackson, 1992), according to US EPA Pesticide Assessment Guidelines, Subdivision N, Paragraph OPP 163-1. The results indicated that highest adsorption was observed in loam. Lower adsorption was observed in clay loam, loamy sand and sand. From the K_aoc values of the four different soil types, a Koc of 136.06 L/kg was calculated for Bronopol. According to the classification developed by FAO (2000) and recommended by US-EPA for the mobility in soil, Bronopol is considered as moderately mobile.

Additionally, the adsorption of 14C-Bronopol onto and desorption from four different soil types was investigated according to US EPA Pesticide Assessment Guidelines, Subdivision N, Paragraph OPP 163 -1 [The Boots Company 1992].

The results indicated that highest adsorption was observed in loam (< 26 %). Lower adsorption was observed in clay loam (< 25 %), loamy sand (< 13 %) and sand (< 8 %). Moreover, the test material was instable under test conditions and the observed degradation varied in the four soil types.

Adsorption of Bronopol and/or its degradation products was correlated to the soil pH. Higher adsorption was observed in alkaline soil (loam) than in acidic soil (clay loam) due to differences in the degradation pathway of Bronopol.

In fact, in the more alkaline loam soil, relatively non-polar degradation products (such as 2 -bromo-2 -nitroethanol) were observed which might be potentially more adsorptive than the relatively polar product (such as tris-(hydroxyl-ethyl)-nitromethane) formed in the more acidic clay loam soil.

Conclusively, adsorption to soil differs among the various soil types, however, the adsorption potential of Bronopol is generally low, indicating no obvious risk to the soil compartment.

Additionally, the Koc has been estimated by QSAR estimation using KOCWIN V.2.01, which is integrated in Epi Suite v4.11. A Koc of 1 was estimated using the MCI method. This finding supports the results of the experimental study that stated out that bronopol is unlikely to adsorb to the solid phase.

The Koc of bronopol is estimated as 5, using a water solubility of 2.0E+5 mg/L and a regression-derived equation [HSDB 2009]. This estimated Koc value suggests that bronopol is expected to have very high mobility in soil.